Unconjecturable

a. (UN-¹ 7 b.)

1806.  J. Wilson, Lett., in Mem., iv. (1879), 78. I have long been conjecturing the reason of your unconjecturable silence.

1829.  Bentham, Justice & Cod. Petit., 88. Not to speak of an unconjecturable variety of other circumstances.

1863.  Lytton, Caxtoniana, I. 308. Thus Faith … loses itself no more among the phantom shadows of the Unknown and Unconjecturable.

  So Unconjecturability.

1802–12.  Bentham, Rationale (1827), IV. 37. From this unconjecturability, two … advantages accrue to the partnership.